Among the electronic devices comprising at least a part based on material provided by organic chemistry, organic light emitting diodes (OLEDs) have a prominent position. Since the demonstration of efficient OLEDs by Tang et al. in 1987 (C. W. Tang et al., Appl. Phys. Lett. 51 (12), 913 (1987)), OLEDs developed from promising candidates to high-end commercial displays. An OLED comprises a sequence of thin layers substantially made of organic materials. The layers typically have a thickness in the range of 1 nm to 5 μm. The layers are usually formed either by means of vacuum deposition or from a solution, for example by means of spin coating or jet printing.
OLEDs emit light after the injection of charge carriers in the form of electrons from the cathode and in form of holes from the anode into organic layers arranged in between. The charge carrier injection is effected on the basis of an applied external voltage, the subsequent formation of excitons in a light emitting zone and the radiative recombination of those excitons. At least one of the electrodes is transparent or semitransparent, in the majority of cases in the form of a transparent oxide, such as indium tin oxide (ITO), or a thin metal layer.
Among the matrix compounds used in OLED light emitting layers (LELs) or electron transporting layers (ETLs), important position have the compounds that comprise at least one structural moiety comprising a delocalized system of conjugated electrons and/or compounds which comprise atoms bearing free electron pairs. During last decade, a particular attention attracted matrix compounds showing various combinations of both functional features—the presence of free electron pairs, localized for example on atoms of 15th-16th group of the Periodic Table, as well as the presence of delocalized systems of conjugated electrons, provided most frequently in form or unsaturated organic compounds. Currently, broad spectrum of electron transport matrices is available, ranging from hydrocarbon matrices comprising only homocyclic aromatic systems and/or double and triple carbon-carbon bonds, to matrices comprising highly polar groups selected from phosphine oxide and diazole.
Electrical doping of charge transporting semiconducting materials for improving their electrical properties, especially conductivity, is known since 1990s, e.g. from U.S. Pat. No. 5,093,698 A. An especially simple method for n-doping in ETLs prepared by the thermal vacuum deposition, which is currently the standard method most frequently used, e.g. in industrial manufacture of displays, is vaporization of a matrix compound from one vaporization source and of a highly electropositive metal from another vaporization source and their co-deposition on a cool surface.
Besides the use of n-dopants in mixed layers comprising a matrix and the dopant, an alternative way for device design is the use of n-dopants in form of a layer adjacent to layer of the matrix material which has to be doped.
There is an inherent discrepancy between the need for stronger n-dopants and high reactivity and sensitivity of such dopant to ambient conditions, which makes their industrial application generally and, specifically, the fulfillment of contemporary quality assurance (QA) requirements difficult.
The state of the art is briefly summarized in a previous application published as WO2015/097232, in which applicants successfully addressed some of the above mentioned problems. Despite continuing progress in this field, there is still an unmet demand for strong n-dopants, able to provide high-performance semiconducting materials with a broad spectrum of matrix compounds, under mild and highly reproducible processing conditions.
It is an object of the invention to overcome the drawbacks of the prior art and to provide metallic layers with improved performance.
The second object of the invention is to provide electronic device utilizing the metallic layer adjacent to a substantially covalent layer.
The third object of the invention is to provide process for preparation of the improved metallic layer as well as for preparing electronic device comprising the improved metallic layer.
The fourth object of the invention is providing air stable metal compositions allowing easy preparation of the improved metallic layer and/or utilizable as advantageous intermediate in preparation of electronic devices comprising the improved metallic layer.